I have no idea why yours died Indy. It could have been bad water quality(would have to have been really bad though), over feeding, or maybe they were stung by the lion(I seriously doubt it thoguh). Its almost impossible to tell what killed them now.
All I do is feed mine every 2-3 days, just until they look full(not too full though) and do 50-60g water changes once a month to keep the nitrates down. IME they're very easy, hardy fish to keep.